Development, homeostasis, and function of Treg cells depend on dendritic cells (DCs). DCs also play a critical role in the development and activation of conventional T cells. One challenging task we now facing is to understand how DCs can discriminate these distinct functions. The goal of this proposal is to investigate the mechanisms by which protein kinase A (PKA) regulates the development and homeostasis of Treg cells through PKA-DC axis, and to explore whether we can control autoimmune diseases such as typr 1 diabetes (T1D) through modulating PKA activity in DCs. Our recent preliminary data show that: 1) DC-specific ablation of PKA regulatory subunit R11 (termed here as the DC-PKAR11 ko mutation) results in a markedly increase in total number of Treg cells;2) PKAR1a ko DC (termed as PKAhi-DCs) exhibit an activation phenotype and produce high levels of IL-2 and IL-10;and 3) NF-kB is constitutively activated and expression of vitamin D receptor (VDR) significantly up-regualted in PKAhi-DCs. Based on these data, we will test the hypothesis that PKA activation in DC promotes thymic Treg development and mature Treg cell homeostasis through the NF-kB and VDR pathways, and modulation of PKA activity in DC may increase the number of Treg cells, consequently treating and preventing autoimmune diseases such as T1D. Our specific aims are: 1. To investigate the role of PKAhi-DCs thymic Treg cell development and peripheral Treg cell homeostasis 2. To investigate the role of PKAhi-DCs in prevention and treatment of T1D 3. To elucidate the molecular mechanisms by which the DC-PKAR11 ko mutation influences DC function in Treg development and homeostasis Result from this study will not only bring further insight into the mechanisms by which DCs regulate Treg development and homeostasis but also provide a new avenue to modulate DC function in the treatment and prevention of autoimmune diseases such as T1D. PUBLIC HEALTH RELEVANCE: This proposal will investigate the regulatory mechanisms by which PKA signaling in dendritic cells (DC) controls homeostasis of regulatory T (Treg) cells. Treg cells are known to play a pivotal role in prevention of autoimmunity such as type-1 diabetes (T1D). Thus, completion of this project may bring insight into our understanding of immune regulation and provide a new target for the prevention and treatment of autoimmune diseases such as T1D.